1. Field of the Invention
The present invention relates to a prepreg for laminate, a laminate prepared from same, and a process for the production of a printed wiring-board using the same.
2. Discussion of the Background
In recent years, printed wiring-boards have been made to have a high density and have been multi-layered, in response to the miniaturization and the high performance demands of electronic devices. In a double-sided board or a multi-layer board having multiple circuitry layers, so-called via holes are usually formed by a perforating step through drilling and copper-plating of hole inner walls to connect circuitry layers. At present, a multilayer printed wiring-board having blind via holes (IVH) has been employed in many cases to satisfy the high density requirements.
In a method in which drilling is employed to form a via hole, it is difficult to form a drilled hole having a small diameter, and the formation of a hole having a small diameter is limited. As a solution thereof, a laser irradiation or perforation with a plasma using an outer layer copper foil of a laminate as a mask has been proposed. However, in a laminate formed by using a conventional glass fabric prepreg, there is a big difference in a heat decomposition temperature between a resin and a glass fiber. Thus, it has been a difficult technique to perforate both components without damaging them. Further, a through-hole plating step is conducted in a copper clad laminate obtained by the conventional laminate-pressing method. Consequently, in the outer layer conductor, the copper thickness of the copper plate is added to the thickness of the copper foil, increasing the thickness of copper. Thus, it is difficult to form a fine pattern.
In order to address this problem, a method in which a copper foil of a copper clad laminate is removed through etching and then a copper plate is applied again to form a conductor layer and a method in which a prepreg and an inner layer material are laminate-pressed, the surface is treated mechanically (physically) and a circuit is formed through copper-plating have been also proposed. In these methods, an adhesion strength between a resin and a copper plate is not satisfactory. Thus, the use of the resulting product as a printed wiring-board has been problematic. Especially, methods using a grinder, a laser beam and the like have been studied as methods of roughening a surface of a laminate physically and mechanically. However, in the former method, a uniformity and a fineness are limited. In the latter method, an accuracy is good, but the production efficiency is poor. Thus, it is not practical.
Japanese Laid-Open (Kokai) No. 295,554/1993 proposes a method in which a prepreg obtained by pulverizing a resin cured upon dispersing a plating catalyst, mixing the resulting powder with a varnish and impregnating the mixture into a substrate is laminated. However, this method involves problems in which properties such as a heat resistance, electrical insulation properties and the like are decreased because the plating catalyst remains and a nitrile rubber is used. Thus, this method can no longer be applied to printed wiring-boards, which in recent years have required a high density.
Meanwhile, a multi-layer printed wiring-board has been developed in which insulating resin layers are built up alternately on a conductor layer without using the conventional laminate-pressing method. However, in this method, it is necessary to introduce a novel equipment, involving a high cost. Further, this method is problematic in respect of reliability with regard to the uniformity of the thickness between insulating resin layers, the adhesion with the inner layer material and incorporation of foreign matters when coating an insulating resin, in comparison with the laminate-pressing method.
Under the above-mentioned circumstances, the problems are to provide a prepreg for laminate and a laminate that satisfy a high density, a heat resistance, electrical insulation properties and an adhesion strength to a conductor layer at the same time, a multi-layer printed wiring-board which meets a high density and which is excellent in a heat resistance and electrical insulation properties upon utilizing the conventional production equipment and method of laminate-pressing, and a process for producing the same.
In order to solve the above-mentioned problems, the present inventors have assiduously conducted investigations, and have consequently found that a prepreg for laminate, a laminate, a printed wiring-board and a multi-layered board obtained by using the same, as described below, exhibit quite excellent properties. These findings have led to the completion of the present invention.